Heater for boilers of the vertical type



July 1931,

Filed Nbv.

2, 1928 4 Sheets-Sheet 2 am v John W 6' 4/1/70 INVENTOR Jul 28, 1931'.J. W. CANNON 1,8 ,1 0

HEATER FOR BOILERS OF THE VERTiCAL TYI E Filed Nov. 22, 1928 4Sheets-Shee 5 INVENTOR JOHN W. CANNON Bx mam/K 7 ATTORNEY July 2 8,1931.

J. w. cANNo N HEATER FOR BOILERS OF THE VERTICAL TYPE Filed Nov.

1928 4 SheetsShee 4 INVENTOR JOHN W. CANNON. BY fivmw C- map/ 7 ATTORNEYPatented July 28, 1931 PATENT OFFICE JOHN W. CANNON, F PLAINEIELD, NEWJERSEY HEATER FGR BOILERS OF THE VERTICAL TYPE Application filedNovember 22, 1928. Serial No. 321,254.

This invention relates to heaters, and more particularly to waterheaters of the domestic house-heating boiler type wherein the water iscontained within a vertical annular space,

the interior of the said space constituting or being furnished witha-combnstion chamber for heating the water. i

It is the general purpose and object of the invention to provide aheater of the character referred to which will secure a very highefiiciencyfronl the combustion fuel, thereby producing economy inoperation. A further object of the invention is to provide aconstruction of heater which, while realizing 5 such efiiciency inoperation, will be extremely sim )le of construction and economical ofpro uction.

' Further objects of the invention will appear hereinafter and will berealized in and '20 through the construction and arrangement of partsshown in the drawings. wherein Fig. 1 represents a central verticalsectional view through a heaterconstructed in accordance with andembodying my invention; Fig. 2 a transverse sectional view correspondingto .the line 22 of Fig. 1 and looking in the f direction of the arrows;Fi 3 a View, similar to Fig. 1, of a modifie form of heater embodying myinvention; Figs. 4 and 5 are details in section correspondingrespectively to the lines 4-4 and 5- 5 of Fig. 3 and look ing in thedirection of the arrows; Figs. 6 and Z illustrate the adaptability ofour fur- 'nace arrangements to a coal-fired furnace, Fig.7 being atransverse sectional view on tical wall of an annular water heater,thelower ends of the said walls being connected in any suitable mannerto an annular bottom plate 3 which extends inwardly beyond the the topof the outer wall having a central outlet 5 adapted to discharge into aflue 6.

The inner wall 2' is provided at its top with acover wall 7 extendinginwardly to a central .the line 7 -7 of Fig. 6; and Figs. 8 and 9 rep-Referring first to Figs. 1 and 2, 1 denotes inner wall 2. I 4 denotes adome or cover for,

leading to the thermostatic device installed opening 8 which isconnected by a short flue 9 with a transversely extending chamber 10having its outer wall 11 spaced from the wall 1 and connected by fines12 with the chamber 13 provided below the dome 4. The inner wall 2 andits cover 7 provide a chamber A' surrounding the combustion chamber.

- 14= denotes the inner vertical wall and 15 the outer vertical wall ofa combustion chamber, the wall 15 being provided with a closed top 16spaced from the top of the wall 14, the parts 14 and 15 being soarranged that an annular space 17 is provided therebetween and the wall15 being provided at the bottom with-a plurality of outlet openings 18.The pints 14, 15 and 16 of the combustion chamr are mounted upon anannular plate 19, preferably'of metal, the outer portion of the platebeing secured to the inner portion of the bottom plate 3, as by meahs ofbolts 20.

To the bottom of the plate-19, insulating material is applied, asindicated at 21; and an angular ring 22 is secured to the inner edge ofthe bottom of the plate 19, the said ring being of somewhat greaterdiameter than the central opening in the said plate, thereby providingwithin the ring a seat 23 for the upper end of a casing, indicatedgenerally'at 24.

This. casing is shown as substantially circular in section and comprisesan intermediate contracted portion 25, with an upwardly flaring orinverted trusto-conical portion 26 extending therefrom and having itsupper edge seated within the ring 22; also with a lower frusto-conicalportion 27 which merges with a bottom cylindrical portion 28 from whichthere extends an air supply duct 29, the outer end of which is providedwith a damper 3O operated by a flexible connection,

,such as a chain 31, which in turn is connected with and operated by anysuitable temperature-controlled mechanism of the thermostatic order. Thedamper-operating portion of the said mechanism is indicated conventionally at 32 and is operated by wires 33 in theparticular place thetem erature wil such as indicated herein are the Honeywell control, andthe control known to the trade as the Regitherm.

Projecting into the duct 29 is a gas supply pipe 34 discharging into aheader 35 located in the part 28 of the casing 24. This pipe is providedwith a valve 36 equipped with a thermostatically-operated control 37similar to the control 32 and provided with the wires 38. The showing ofthe valve 36 in Figures 1 and 3 is conventional. It is understood thatthe thermostatic control 37 may be applied to any slow-opening valvesuch as that which is illustrated in Figures 8 and 9. Control member 37may be identical withmember 32, but is shown separately for contube 40is arranged centrall with respect to the tubes 39 and is provide with aflattened delivery end 41'. The flattened ends 40 and 41 of the burnertubes provide elongated slots 42. p

Within the parts constructed and arranged as described, the operationwill be as follows :.Gas will be supplied through the pipe 34 in theusualmanner to the header 35 and will be ignited as it issues from theslots 42. A pilot burner P which is to be lighted before the furnace isstarted is shown at P in Figure 1 and in Figure 3. The streams of gas,being delivered at the contracted portion of the Venturi tubeconstituted by the parts 26 and 27, will entrain in a most eflicientmanner the air supplied to the said tube through the duct 29, and theignited mixture will be burned in the combustion chamber provided by theparts-14 and 17 inclusive. The parts will be so constructed andproportioned that complete combustion will be secured within thechamber,-the best results being accomplished when the end of the flamereaches the ports 18; andthe aggregate area of the said ports should bepreferably as great as the cross sectional area of the annular space 17.

The parts 14, 15 and 16 are made of material having a thermalconductivity greater than 0.006 calorie/cm /C./sec. such as siliconcarbide. This material also has a high emissivity, which has been foundin some cases a to be about'97 percent of that of a black body. Fusedalumina is another material which. has a comparatively high thermalconductivity and which I might also use in constructing the combustionchamber. It is particularly structed of good conducting material such asmentioned. This is not so much the case with the inner cylinder 14. Thismay be constructed of any refractory which will withstand high flame temeratures. It is essential that the inner sur ace of 14 should be heatedto incandescence to insure complete combustion of the fuel and to reducethe amount of soot which is formed as a result of incomplete combustion.

The thermal conductivity of fire clay may be given as 0.004 calorie/cm/C./sec. while that of silicon carbide is said to attain a value abouteight times as great or 0.034 in the same units at certain hightemperatures.

The Water and vapor between the shells or casings 1 and 2 will be heatedmainly by radiation from the walls 15 and 16 of the outer member of thecombustion chamberand will also be heated by the products otcombustiondelivered through the ports 18 and passing through the chamber A, flue8, transverse chamber 10, flues 12, and chamber 13. The vapors thusgenerated will be conducted to the point or points of use by means ofany suitable pipe installation (not shown).

The particular construction and arrangement of the burner parts 35-42with reference to the Venturi tube 25, 26 and 27 insures the entraininfgof a large quantity of air by the gas issuing from the burner slots,With a corresponding quick commingling of adequate proportions of airand gas and a corresponding quick combustion of the mixture thusenabling me to reduce the length of the combustion chamber and of themembers constituting the same. Furthermore, the burners 39*, 41 and theheader 35 are located where they are exposed to the. inner combustionchamber member 14 and are therefore subjected to the radiant heat of thesaid chamber. I

By the use of the enlarged header 35, the gas from the pipe 34 on itsway to the burner tubes is retained for a while in a heated zone wherebythe gas is preheated before delivery to the burner tips. .The a airsupplied through the Venturi casing or tube is also preheated by contactwith the walls of the casing, which are themselves heated by radi-'ation as above described. The result is that I amenabled to produce ahigher tempera- .ture in the combustion chamber and to improve theefiiciency of the heater as a whole. In fact, I have been able, with aheater of the type shown herein, to convert fifty per cent or more ofthe total heat of combustion into the form of radiant energy and to se-,cure a very high rate of vapor or steam generation with a comparativelysmall rate of combustion of the gaseousfuel.

The damper 30 and the valve 36 will be operated by thermostatic means,Figures 8 and 9 show one type of slow opening valve i essential featureof the valve being to proa cylindrical casing 44 is provided, the uportion of said casing having slots 45 w 10b 1 vide that the rate offuel feed to the burner shall be slow at first and progressivelyincrease until the normal firing rate is reached, as the combustionchamber becomes heated. In Figures 8 and 9, 36 indicates the valve as awhole. The valve is opened by raising the lever which is shown in Figure8 as piv oted at 71. Lever 70 operates the curved arm 80 and connectinglink 81 to raise the cylinder designated generally as 83. At the start,the passage of fuel is entirely prevented by the seating of portion 72of the cylinder on portion 3 of the valve casing. As soon as thecylinder is raised slightly, free flow of fuel takes place past thisseat however, and in order to restrictthe flow I provide a secondaryseat of portion 83 of the cylinder against portion 82 of the casing.This seat is maintained at all times. The cylinder is cut away as shownat 74, however, thus providing a passage up thru the hollow center 76 ofthe cylinder into the annular chamber 84 and as the cylinder is raisedthe proportion of the aperture 74 above the rin 82 is increased, thuspermitting increased flow of fuel.

In Figs. 3-5 inclusive I have shown a modification of my invention inwhich the parts 318 are identical, or substantially identical, with thelike-numbered partsun the preceding views. Instead of placing 1nsulatingmaterial below the annular plate which supports the combustion chambersections, I support the lowerend of the section 15, 16 upon an annularslab 43 of silicon carbide or other material having high heat-radiatingqualities and a thermal conductivity greater than 0.006 calorie/cm/C./sec. and extend the plate 3 inwardly to form a support for the innersection 14 of the combustion chamber as indicated at '3.

Instead of using a Venturi tube for the easing which receives the burnerand its header, er

receive heated air from an annular chamber 46 which is provided belowthe plate 3, 3 and above an annular plate 47, the central aperture ofwhich plate 47 receives the upper portion of the casing 44. In bothforms of my invention, the heater 18 supported by a flanged annular base48 and legs 49, The bottom of the plate 47 and the outside of the casing44 are covered with insulating material, indicated at 47a and 440respectively.

The air to be heated is supplied to the chamber 46 through openings50*.in the cylindrical outer wall 50 of the chamber, which openings arecontrolled by a ring'damperbl surrounding the wall 50an d provided withopenings 51 adapted to register more or less with the openings 50, thesaid damper being tion 47.

provided with a lug 52 connected by a rod 53 with thethermostatically-operated control 32.

" Gas is supplied by a pipe 34 provided with a thermostaticallycontrolled valve 36 such as has already been described, to an annularheader 54. From this header, burner tubes 55 extend upwardly within thecasing, being provided with flattened ends 55' having burner slots 56,the slots being preferably located at substantially the bottoms of theopenings 45 for heated air.

Because of the material of which the slab 43 is composed, the airpassing throu h the chamber 46 will be heated in a most eiicient manner,and loss of heat from such chamber by radiation will be prevented by theinsula- The header 54 and burner tubes 55 will also be heated byradiation from the combnstionchamber, and the loss of heat by radiationfrom the casing 44 will be minimized by reason of the insulation 44. Thegas issuing through the burner nozzles and blowing ast the air ports 45will pull the hot air out o the chamber 46 and the velocity of gasacross the ports will control the amount of hot air drawn into thecombustion chamber. It is necessary to inject by the action of theburner orifices or nozzles a large amount of air, substantiallyproportional to the flow of the gas in both forms of the invention,because the air requisite-for roper and efficient combustion cannot be 0tamed by the action of a draft through the fiues 6, the draft beingbroken, as shown in the drawings. The arrangement of the burner nozzleswith reference to the air supply, in both forms of my invention, insuresthis large and proportional supply of air to the combustion chamber.Furthermore, by the manner of forming the mixture of gas and air, thereis no danger of the gas firing, back to the burner orifices or outletsin the event that the size of the gas fire is reduced to a minimum or inthe event the gas pressure is greatly reduced.

The form 0 my invention illustrated in Figures 6 and 7 shows anadaptation of my invention to furnaces originally built for burningcoal. The arrangement of the combustion chamber is shown similar to thatin Figure 3. The chamber 46' for preheating the combustion air ishowever, wholly within the furnace. Walls 44?) and 47 b of insulatingrefractory material tend to reduce the loss of heat from the casing 44'and from the air preheating chamber respectively. The amount of airwhich is admitted is varied by variations in the rate of gas flow aspreviously described and may be additionally controlled by means of thethermostatically operated damper. Gas is supplied by a slow openingthermostatically operated valve as previously described. The arrows inFigure .6 show the path of the products of combustion through the upperportions of the furtogether after introduction into the furnace.

' The stand 90 may also be introduced in sections and bolted togetherafter introduction into the; furnace. r

In the form of my invention shown in Figures 3 to 7 the refractories ofwhich the combustion chamber is composed may be inserted chamber as inpractice the combustion chamber is composed of sections which can beinserted through the door opening.

In the alternate form of my invention, the combustion chamber may beinstalled u on the bottom of the heater and the water 1' ac et set inplace around it. This construction simplifies the installation of therefractory material and increases the efliciency of the heating unit inthat it eliminates the need for leaving door space in the sidewalls ofthe heater, thus permitting this space to be used as efiective heatinsurface.

On account of t e break in draft between flue sections 5 and 6 and thereduction in temperature of the combustion gases by the transfer of heatto the surounding water or steam,

J the natural draft through the combustion chamber is very small and theflow of air can be made very largely dependent on the induction causedby the flow .of gas. vWhere this advantage is fully realized thethermostatic connections to the air controlling damper may bedispensedwith and the damper permanently adjusted to anydesired position.

A prineipal advantageof my fuel burning arrangement is that it securessubstantially com lete combust-ionof th'efuel at all times. Per ectcombustion is particularly hard to obtain when a large flow of gas isturned on while the combustion chamber is cold. This is because in suchcases the rate of combustion ed to incandescence after which a greatlyincreased rate of gas flow'is permissible.

This adjustment of the rate of gas flow to produce complete combustionat all times 1s obtained by the use of the slowopening valve has shownin Figure 8 where the chain 8653s raised slowly, as for instance, bywinding around a drum (not shown) driven at a suitable speed by a motorin the thermostatically controlled element 37 The rate of raising thischain and the attached lever is such as to cause slow opening of thevalve thus giving suitable regulation of the gas flow to the coinbustionchamber to secure the result described.

After the walls of my combustion chamber 0 have been heated toincandescence it is pos sible to secure complete combustion of gas inthe chamber at a very high rate ,due to the accelerated velocity ofoxidation at high temperatures and the speed with which the heatliberated within the combustion chamber is transmitted through the Wallsand radiated to the Water containing casing. I have found it possible tocontinuously liberate heat in this way for example at a rate in excessof400,000 B. t. 11'. /hr. cu. ft. of combustion chamber when firing citygas without damage to my heater. I I

While my invention has been described primarily with reference to adomestic heater for water or-steam, my improved heater is also obviouslyadaptable to a wide variety of other uses, such as heating an airheating furnace, supplying hot gases for drying purposes, etc., and itis not my desire to consider it limited to application for the specificpurposes illustrated. I

I claim:

1. In a heating device, a combustion chamber having an inner wall ofcontinuous nonmetallic refractory material capable of being heatedtoincandescence, said inner wall surrounding the hottest portion of saidcombustion chamber, an outer wall of continuous .non-metallic refractorymaterial of thermal conductivity in excess of 0.006 calorie/cm C./sec.',said outer wall surrounding the .innor one to form anannular passage forthe products of combustion, a container for ma- "terial to be heatedsubstantially surrounding the combustion chamber and adapted to beheated by radiation therefrom and by contact with the products ofcombustion, and

terial to be heated substantially surrounding the combustion chamber andadapted to be heated by radiation therefrom and by contact with theproducts of combustion, means for preheating the gas and air forcombustion, and means for introducing the preheated gases into thecombustion chamber.

means for introducing a combustible mixture 3. In a heating device, acombustionchamher having an inner wall of continuous nonmetallicrefractory material capable of be: ing heated to incandescence, saidinner wall surrounding the hottest portion of said com: bustion chamber,an outer wall of continuous non-metallic refractory material of thermalconductivity in excess of 0.006 calorie/ cm"/9C./sec., said outerwallsurrounding the inner one to form an annular passage for the products ofcombustion, a container for material to be heated substantiallysurrounding the combustion chamber and adapted to be heated by radiationtherefrom and by contact with the products of combustion, means forintroducing a combustible mixture into the combustion chamber, means forigniting said mixture, and a thermostatically operated device forregulating the supply of fuel.

4. In a heating device, a combustion chamber having an inner wall ofcontinuous nonmetallic refractory material capable of being heated toincandescence, said inner wall surrounding the hottest portion of saidcombustion chamber, an outer wall of continuous non-metallic refractorymaterial of thermal conductivity in excess of 0.006 calorie/cm C./sec.,said outer wall surrounding the innerone to forman annular passage forthe products of combustion, a container for material to beheatedsubstantially surrounding the combustion chamber and adapted to beheated by radiation therefrom and by contact with the products ofcombustion, means for introducing a combustible mixture into thecombustion chamber, means for igniting said mixture, and athermostatically operated glow-opening valve controlling the supply of5. In a heating device, a combustion chamber having an inner wall ofcontinuous nonmetallic refractory material capable of being heated toincandescence, said inner wall surrounding the hottest portion of saidcombustion chamber, an outer wall of continuous non-metallic refractorymaterial of thermal conductivity in excess of 0.006 calorie/cmv C./secsaid outer wall surrounding the inner one to form an .annularpassage forthe products of combustion, a container for material to be heatedsubstantially surrounding the combustion chamber and adapted to beheated therefrom and by contact with the roducts of combustion, meansfor introducmg a combustible mixture, a'thermostatical- 1y 0 erateddevice for regulating the sup ly of uel, and means for preventing the 11flow of fuel until the combustion chamber has been heated toincandescence. 6. In a heating device, a combustion chamber having aninner wall of continuous nonmetallic refractory material capable ofbeing heated to incandescenc'e, rounding the hottest portion of saidcombustion chamber, an outer wall. of

said inner wall sur tion chamber,

nonmetallic refractory material of thermal conductivity in excess of0.006 calorie/cm C./sec., said outer wall surrounding the inner'one toform an annular passage for the products of combustion, a container formathe combustion chamber, and a fuel inlet with an air inlet so disposedin relation thereto as to cause air for combustion to be drawn in andmixed with the fuel.

7 In a heating device, a combustion chamher having an inner wall ofcontinuous nonmetallic refractory material capable of being heated toincandescenoe, said inner wall surrounding the hottest portion of saidcombustion chamber, an outer wall of continuous non-metallic refractorymaterial of thermal conductivity in excess of 0.006 calorie/cm C., sec.,said outer wall surrounding the in ner one to form an annular passagefor the products of combustion, a container for material to be heatedsubstantially surrounding the combustion chamber and adapted to beheated by radiation therefrom and by contact with the products ofcombustion, means for introducing a combustible mixture into thecombustion chamber, a fuel inlet with an air inlet so disposed inrelation thereto as to cause air for combustion to be drawn in and mixedwith the fuel at a rate dependent upon products of combustion, acontainer for ma terial to be heated substantially surrounding thecombustion chamber and adapted to be heated by radiation therefrom andby contact with the productsof combustion, means for introducing acombustible mixture into the combustion chamber, a fuel inlet sodisposed in relation thereto as to cause air for combustion to be-drawnin and mixed with the fuel, means for igniting said mixture, and athermostatically operated slow-opening valve controlling the supplyof'fuel.

9. In a heating device, a combustion chamber having an inner wall ofcontinuous nonmetallic refractory material capable of being heated toinca'ndescenoe, said inner wall surrounding the hottest portion of saidcombusan outer wall of. continuous non-metallic refractory material ofthermal continuous conductivity in excess of 0.006 calorie/m7 iii C.,sec., said outer wall surrounding the inner one to form an annularpassage for the products of combustion, a container for material to beheated substantially surroundingthe combustion chamber and adapted to beheated by radiation therefrom and by con tact with the products ofcombustion, means for introducing a combustible mixture into thecombustion chamber, means for igniting said mixture, and thermostaticcontrols on the conduits supplying fuel and air respectively.

10. In a heating device, a combustion chamber having an inner wall ofcontinuous non-metallic refractory material capable of being heated toincandescence, said inner wall surrounding the hottest portion of saidcombustion chamber, an outer wallof continuous non-metallic refractorymaterial of thermal conductivity in excess of 0.006 calorie/cm /C./sec.,said outer Wall surrounding the inner one to form an annular passage forthe products of combustion, a container vfor material to be heatedsubstantially surrounding the combustion chamberand adapted to be heatedby radiation therefrom and by contact with the products of combustion,means for introducing a combustible mixture ,into

- i the combustion chamber, a fuel inlet so; dis- 30 i combustion to bedrawn in and mixed with posed in relation thereto as to cause air forhaving a thermal conductivity in excess of 0.006 caloric/cm /C./sec., aburner for supplying a combustible mixture to said com bustion chamber,means for igniting said mixture, and a thermostatically operatedslow-opening valve controlling the supply of fuel.

12. In a heating device, a double-wall combustion chamber adapted toradiate heat from its walls to an adjacent body, a burner which maintans intense combustion within the inner wall of said chamber, means forintroducing a combustible mixture into thecombustion chamber, a fuelinlet so disposed in relation thereto asto cause air for com-,

bustion to be drawn in andmixed with the fuel, means for igniting saidmixture, and

a thermostatically operated slow-openingvalve controlling thesupply offuel.

-tion -chamb er of"continuous nonnnetallic refractorylabove said burner,a pilot ignition arrangement adjacent to said burner, a therdevice, acombustion mostatically controlled valve for admitting gas to saidburner, said valve being so constructed as to open slowly whereby thewalls of the furnace are at first subjected to a gradually increasingtemperature and the combustion of fuel is always approximately completeas the inner wall of the combustion chamber approaches incandescence;means for induging a current of air at the gas outlet to the burnerwhich supply of air is proportional to the supply of gas issuing fromthe outlets.

14. The combination, with a longitudinally extending annular heater, ofa combustion chamber of non-metallic refractory within the said heaterand comprising an inner member and an outer member surrounding andspaced from the inner member and having a cover spaced from the adjacentend of the inner member to provide an annular return passage forproducts of combustion, the outer member having one or more outletopenings at the end thereof opposite its cover, a casing extending fromthe receiving end of the inner member, a gas burner in said casing, anair supply for said casing, said supply of air being drawn in by the gasissuing from the fuel outlet for said burner, andthermostatically-controlled means for regulating the supply of air tothe said casing and of gas to said burner.

15. The combination, with a vertically disposed annular heater, of avertically extending combustion chamber within the said heater, a casingextending downwardly from the said chamber and communicating withthebottom thereof, said casing being in the form of a Venturi tube, gassupply tubes with flattened orifices within said casing each providedwith a discharge orifice arranged within the contracted portion of saidcasing, said orifices being arrangedrin a circle substantiallyconcentric with the Venturi' tube,

and means for supplying air to said casing below the contracted portionthereof.

16. 'The combination, with a vertically disposed annular heater, of avertically extending combustion chamber within the said heater,- a casinextending downwardly from the said cham erand communicating with thebottom thereof, said casing being in the formof a Venturi tube, gassupply tubes within said casing-each provided with a discharge orificearranged within the contracted portion of said casing, and means forsupplying air to said casing below the contracted portion thereof, thesaid combustion chamber having .a wall of high heat radiating qualitiesarranged to heat by radiationthe said casing and the air and the burnerytubes therein. a 13. In a gas furnace, a burner, a combus- 17. Thecombination, with a vertically dispgsed annular heater, ofa combustionchamr within the said heater and extending u'pwardly from the lowerportion thereof, a

casing extending downwardly from and communicating with the bottom ofsaid combustion chamber, gas supply tubes with outlets located withinthe said casing, and

means for supplying air into said casing, to mingle with gas from thesaid outlets, the said combustion chamber comprising a wall of highheat-radiating qualities arranged to heat by'radiation the gas and theair in and supplied to said casing.

18. The combination, with a vertically disposed annular heater, of acombustion chamber within the said heater and extending upwardly fromthe lower portion thereof, a casing extending downwardly from thecombustion chamber and communicating therewith, gas supply tubes withoutlets in i said casing, and means for supplying air to said casing,the gas outlets and the air supplying means being so arranged that theamount of air supplied to the casing and to the combustion chamber willbe approximately proportional to the rate of delivery of gas from thesaid outlets into the casing and into said combustion chamberi 19. Thecombination, with a vertically disposed annular heater, of a combustionchamber within said heater and extending upwardly from the lower portionthereof, a casing extending downwardly from the combustion chamber' andcommunicating therewith, the said casing being in the form of a Venturitube, gas supply tubes in said casing having their orifices in thecontracted portion of said tube, and means for supplying air to saidcasing below the gas orifices whereby the amount of air injected intothe combustion chamber by the gas will be approximately proportional tothe rate of flow of gas from the gas orifices.

20. The combination, with a vertically disposed annular heater having alarge central openingwithin the bottom thereof, of an annular plateremovably secured to the portion of the heater surrounding such opening,an upwardly extending combustion chamber supported by said plate, acasing extending downwardly from the central opening in said plate,means for supplying to the combustion-ehamberand through said casing amixture of combustible gas and air, an insulating coating below saidplate and on the outside of said casing, and a preheating chamber forthe gas supply in the lower part of said casing. i

In testimony whereof I affix my signature.

JOHN W. CANNON.-

